The present invention relates to a target for a neutron scattering installation.
FIG. 1 shows an example of a neutron scattering installation for performing various research studies on physical properties using neutrons. In the installation, protons from a proton emitter 1 are accelerated by a linear accelerator 2 to enter into an accumulation ring 3 where the protons are circulated by curving their orbits with a deflecting electromagnet and are increased in velocity using high frequency electric current until required energy can be reached.
The protons thus having the required energy are emitted from the ring 3 to a target 4 where they are brought to collide against liquid heavy metal such as mercury held in the target 4. Fast neutrons generated by nuclear spallation reaction are passed through a moderator such as liquid hydrogen (20 K; 1.5 MPa) held in a moderator container 5 so that they are converted into thermal or cold neutrons suitable for research purpose; these are guided via a beam line 6 to a laboratory 7.
FIG. 2 shows a conventional target for a neutron scattering installation which comprises a container body 8 arranged to counter a proton beam P, which advances approximately horizontally, and a partition 9 having its opposite edges contiguous with a lower inner surface portion of the body 8 and extending from a base end of the body 8 to a position near a forward end of the body 8.
The container body 8 has, at its base end, inflow and outflow ports 11 and 13. The inflow port 11 serves to communicate outside of the body 8 with a liquid-heavy-metal incoming passage 10, which is a space defined between the inner surface of the body 8 and a lower surface of the partition 9. The outflow port 13 serves to communicate outside of the body 8 with a liquid-heavy-metal return passage 12, which is a space defined between the inner surface of the body 8 and an upper surface of the partition 9.
The inflow port 11 is connected with a discharge port of a pump 14 and the outflow port 13 is connected with a suction port of the pump 14 via a heat exchanger 15. Thus, the pump 14, inflow port 11, incoming and return passages 10 and 12, outflow port 13 and heat exchanger 15 compose a closed loop which is filled with mercury M as liquid heavy metal.
In the target shown in FIG. 2, fast neutrons are generated by collision of the protons against the mercury M, which flows via the incoming passage 10 to an inner forward end of the container body 8. The mercury M having received heat from the nuclear spallation reaction is then guided via the return passage 12 to the heat exchanger 15 so as to be cooled down.
However, in the system shown in FIG. 2, the whole of the mercury M supplied to the inflow port 11 makes up a mercury stream which flows via the incoming passage 10 to the inner forward end of the body 8 and turns back via the return passage 12, so that stagnation and/or re-circulation flows R tend to occur near the inner forward end of the body 8. Constant stagnation of the mercury M may lead to occurrence of local increase in temperature (hot spots).
Since the mercury M is brought to continuously flow at higher flow rate in the container body 8 so as to remove the heat caused by nuclear spallation, extremely high burdens are applied on cooling means of, for example, the mercury circulation pump 14 and heat exchanger 15, which makes it difficult to cope with nuclear spallation reaction having higher heat generated.
The present invention was made to solve the above problems and has its object to provide a target for a neutron scattering installation which can provide a stead and highly uniform stream of liquid heavy metal throughout in the system.
In a target for a neutron scattering installation according to any of claims 1 to 3 of the invention, the flow of the liquid heavy metal from the liquid-heavy-metal inflow port toward the inner forward end of the container body is rectified by a plurality of incoming-passage guide vanes installed closer to one side in the container body, and the flow of the liquid heavy metal from the forward end of the container body toward the liquid-heavy-metal outflow port is rectified by a plurality of return-passage guide vanes installed closer to the other side in the container body, thereby suppressing occurrence of stagnation and/or re-circulation flows of the liquid heavy metal in the container body.
In a target for a neutron scattering installation according to claim 2 of the invention, the container body in which the liquid heavy metal flows is covered with a container outer shell, thereby preventing any leakage of the liquid heavy metal to outside as may be caused by damage of the container body.
In a target for a neutron scattering installation according to claim 3 of the invention, the container body in which the liquid heavy metal flows is dually covered by container intermediate and outer shells, thereby preventing any leakage of the liquid heavy metal to outside as may be caused by damage of the container body.